This invention relates to automatic small flow control valves which can be used in place of needle valves for the fine control of liquid or gaseous fluid in a process system.
Quite often chemical processes require the control of corrosive or poisonous fluids. Conventional needle valves have stuffing boxes which are prone to leakage, which in turn can create a substantial health hazard to operating personnel.
Flow control valves using a diaphragm seal (see my U.S. Pat. No. 4,549,719) eliminate the need for packing. However, the travel is severely limited as it must stay within the elastic deflection range of the selected diaphragm material. This then excludes finely tapered, splined or grooved needle valve plugs, since these devices require a relatively large valve travel. Simple valve orifices shown in U.S. Pat. No. 4,549,719, again, are limited by the inability to drill small enough holes into a sometimes hard metal alloy. It is for this reason that the application of diaphragm sealed valves has been limited generally to a Cv number of 0.03 where the Cv coefficient defines the number of US gallons per minute of water passing an orifice or valve at a pressure loss of one pound per surface inch.
My present invention overcomes this limitation by providing for the insertion of a flexible valve member whereby the grooved portion which is normally located parallel to the cylindrical axis of a needle plug, is now located approximately parallel to the surface of the sealing diaphragm and therefore can be covered or uncovered by a relatively short motion of the sealing diaphragm.
Furthermore, by placing an opening through the conical portion of the valve member, a two stage throttling phenomena can be achieved which greatly limits the fluid velocity and associated erosion in such a valve.
Thirdly, the valve insert, as described later in more detail, can be easily exchanged with one of a different opening to suit the users preference for flowing quantities without the need to make time consuming adjustments, calibration or lapping.
All of these advantages are more clearly explained in the following detailed description.